1. Field of the Invention
The present invention relates to a fusing roller device for an electrophotographic image forming apparatus, and, more particularly, to a fusing roller device for an electrophotographic image forming apparatus that can be instantaneously heated so that the temperature of the fusing roller device reaches a fusing temperature within a relatively short time, while using a low amount of current and power.
2. Description of the Related Art
In general, a printer, such as a laser printer, includes a fusing roller device that fixes toner particles transferred on a printing medium. FIG. 1 is a profile cross-sectional view schematically illustrating a conventional fusing roller device for an electrophotographic printer in which a halogen lamp is used as a heat source, and FIG. 2 is a vertical cross-sectional view illustrating a correlation between the conventional fusing roller device and a pressure roller for an electrophotographic printer in which the halogen lamp shown in FIG. 1 is used as a heat source.
Referring to FIG. 1, a conventional fusing roller device 10 includes a tubular fusing roller 11 and a heating portion 12, such as a halogen lamp, that is installed along a center axis of the fusing roller 11. A coating layer 11a of TEFLON® is formed on the surface of the fusing roller 11. The fusing roller 11 is heated by radiant heat transmitted from the heating portion 12.
Referring to FIG. 2, a pressure roller 13 is placed opposite and under the fusing roller device 10. Paper 14 is placed between the fusing roller device 10 and the pressure roller 13. The pressure roller 13 is elastically supported by a spring 13a, and presses the paper 14 passing between the fusing roller device 10 and the pressure roller 13 toward the fusing roller device 10 by a predetermined pressure. A toner image 14a in a powder state formed on the paper 14 is pressed and heated while the paper 14 passes between the fusing roller device 10 and the pressure roller 13. That is, the toner image 14a is fused on the paper 14 as a result of the heat generated by the fusing roller device 10 and the pressure applied by the pressure roller 13.
The conventional fusing roller device, in which a halogen lamp is used as a heating portion 12, as described above causes unnecessary power consumption. Thus, when a printing operation is not being performed, the fusing roller device 10 needs to be cooled by turning off the power. In particular, when the fusing roller device 10 is turned off and then turned on to form an image, a relatively long warm-up time is required. After power is applied to the fusing roller device 10, the fusing roller device 10 remains in a waiting state for a predetermined amount of time (i.e., a first-print-out-time referred to hereinafter as FPOT) until it reaches a desired fusing temperature. This might take from several tens of seconds to several minutes.
In particular, because the fusing roller 11 is heated by heat radiated from the heat source, the conventional fusing roller device 10 has a slow heat transfer speed, and because compensation for a decrease in temperature that occurs due to contact with the paper 14 is slow, the conventional fusing roller device 10 cannot easily adjust temperature scatter. In addition, even in a standby mode in which a printing operation is paused, power must be applied to the heating portion 12 at predetermined time intervals so that the temperature of the fusing roller 11 is maintained at a constant level. Thus, unnecessary power consumption occurs. Because it takes a relatively long time to change from a standby state to an operation mode to output an image, the conventional fusing roller device 10 cannot quickly output an image.
FIG. 3 is a vertical cross-sectional view schematically illustrating another conventional fusing roller device for an electrophotographic image forming apparatus. Referring to FIG. 3, a heating plate 22 is provided in a lower portion of the inside of a cylindrical film tube 21, and a pressure roller 23 is installed opposite to a lower side of the heating plate 22. Paper 14 is placed between the film tube 21 and the pressure roller 23. The pressure roller 23 is elastically supported by a spring 23a such that the paper 14 passing between the film tube 21 and the pressure roller 23 is pressed by a predetermined pressure toward the film tube 21.
The film tube 21 is rotated by an additional rotating device (not shown). A method for locally film the heating tube 21 in a portion where the heating plate 22 contacts the pressure roller 23 has low power consumption, but the method cannot be easily used during a high-speed printing operation.
To solve the problems described above, Japanese Patent Publication No. Hei 11-282294 discloses a heat induction method by which heat is transferred directly to the surface of a fusing roller by providing high-frequency AC from an electrical coil installed around a non-image region, that is, a portion in which toner of the fusing roller does not contact paper. In this method, heat generated from the non-image region flows through the surface of an image region of the fusing roller, and the FPOT is reduced. However, the fusing roller requires an additional circuit to produce high-frequency current, and, as such, the roller mechanism is complicated, which increases costs.
In addition, fusing roller devices disclosed in Japanese Patent Publication Nos. Hei 4-335691, Hei 4-360185, Hei 8-171301, Hei 8-262905, Hei 8-305195, and Hei 9-90811 have structures in which a heat source is provided inside a fusing roller and an overall increase in the size of the heat source is not considered. Also, since a plurality of local heat pipes are provided in the fusing roller, processing and manufacturing thereof are very complicated, and a temperature difference occurs between a portion contacting the heat pipes and a portion not contacting the heat pipes.